As the demand for access to digital media content has increased, content providers have begun searching for more effective solutions to prevent unauthorized redistribution of downloaded digital media content. Digital rights management (DRM) systems have traditionally provided some protection against piracy of copyrighted content. DRM systems seek to control access to copyrighted content by encrypting the digital media content prior to playback by a user, and then subsequently restricting the use of that media content by the user. However, once the digital media content is decrypted and rendered in analog form on a client device, the media content can be readily copied and distributed to unlicensed users.
Digital watermarking has been developed as a tool to help identify those users that redistribute media content illegally. A digital watermark refers to imperceptible information that is embedded in the media content and that uniquely identifies a user. For example, for each streaming session, a content provider can embed a unique watermark in the digital media content streamed to a client device. However, separately embedding a unique watermark in each streamed copy of media content is computationally expensive and impractical in many broadcast and unicast applications, such as video on demand.
To scale digital watermarking for multi-user applications, two or more copies of the same media content can be created, each having different watermark information embedded therein. Each copy can be further segmented into corresponding temporal content segments and streamed to a client device. A unique sequence generated for the client device can then be used by the client device to select between content segments of the different streams to produce watermarked media content that uniquely identifies the user of the client device.
However, if the unique sequence is tampered with, for example, by replacing one stream with another stream, the watermarking technology is unable to identify the user or source of pirated media content.